Thanks be to God (and Google), I was not forced to try my hand at translating Latin. I found the same thing in English. Looking at the corner, it says two things on the outside of the triangle - the Holy Spirit is not the Father, and the Holy Spirit is not the Son. Inside the triangle it says the Holy Spirit is God. And it says the same kind of things looking at the other two corners. So, if I was asking this diagram a few questions:
There are three people here? Yes.
And they are all God? Yes.
There’s only one God, right? Right.
But there’s still three people, right? Right again.
One God, Three Persons? Exactly.